Loudspeaker arrangements in a motor vehicle are used primarily for emitting audio signals. The audio signal sources are, for instance, radios, CD players, MP3 players or DVD players. In addition to that, the loudspeakers are used for emitting acoustical data, of a navigation system, for instance, and/or a parking aid assistance system.
Customary loudspeakers in a motor vehicle are constructed as electrodynamic loudspeakers having permanent magnets. These are relatively voluminous and heavy, and, because of the limited available space in a motor vehicle, this often leads to compromises between installation location and emission characteristic.
A planar loudspeaker is described in Japanese Published Patent Application No. 2004-56564, which is situated behind the roofliner, so that there is a greater degree of freedom with regard to size and shape.
A method is described in German Published Patent Application No. 199 58 836 for improving communications in a vehicle, the voice signals of the passengers of a vehicle being recorded individually for each passenger via a microphone assigned to him within the scope of his seat. The recorded voice signals are amplified separately for each passenger in an input step and are filtered for start level minimization and frequency adjustment. The amplified and filtered voice signals of each individual passenger are submitted to a signal processing that is individual for each output channel, in the form of a propagation delay correction and a level differentiation, for the partition to the output channels and therewith for the partition to the individual components for a voice output device made up of loudspeakers, as a function of the local assignment of the microphone in the vehicle, via which the voice signal was recorded and as a function of the local assignment of each individual loudspeaker of the voice output device in the vehicle, via which the voice signal is to be output, via a summation step and a distribution step. The assignment of the voice signals that were individually processed for each output channel to the individual output channels and thus to the individual loudspeakers of the voice output device takes place via an adjustment stage in which, via a level adjustment and a frequency adjustment, there takes place an adjustment, tuned to each output channel and therewith to each loudspeaker of the voice output device, of the respective voice signal to the spatial conditions of the vehicle and the desired volume. The microphone may be arranged as a directional microphone, in this context. Furthermore, a use as a telephone device having a free assignment of users within the vehicle is suggested. In the case of a use within the framework of telephone processes, the structure of the device makes it possible for a conversation to be assigned, for example, to each seat and, thus, to each occupant. In this context, the reproduction may take place as a controlled process via selected loudspeakers, so that even selected vehicle occupants may participate in the phone conversation. At the same time, it is possible to limit the extent to which other occupants in specific seats overhear the conversation. This is done by switching the incoming signal to loudspeakers chosen for this and by processing it as a fictive, i.e., virtual voice source. The outgoing signal(s) undergo(es) the same process as the signal which is utilized for the internal communication. It is possible to adjust the manner in which specific seats or areas are separated both from the receiving, as well as from the reproduction side, using operating units of the control unit.
An acoustical element is described in PCT International Published Patent Application No. WO 99/56498, that includes at least two porous layers which are electrically conductive or are metallized on one side. Between the two porous layers there is situated an insulated plastic layer which is preferably arranged in two layers, there being a metallic coating between the two layers via which the plastic layer can be loaded to a certain electrical potential. The plastic layer is connected to the porous layers at certain places. Between two such boundary positions there is an air gap between the porous layers and the plastic layer. By applying a signal to at least one porous layer, the plastic layer is then set into vibration, the other porous layer preferably also having the signal, that is in phase opposition, applied to it. This arrangement represents an electrostatic planar loudspeaker.